linux-kernel - [PATCH RFC 5/6] mm: rmap: weaken the WARN_ON in __folio_add_anon

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Date: Fri, 19 Jan 2024 00:10:35 +1300
From: Barry Song <21cnbao@...il.com>
To: ryan.roberts@....com,
	akpm@...ux-foundation.org,
	david@...hat.com,
	linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org,
	mhocko@...e.com,
	shy828301@...il.com,
	wangkefeng.wang@...wei.com,
	willy@...radead.org,
	xiang@...nel.org,
	ying.huang@...el.com,
	yuzhao@...gle.com,
	surenb@...gle.com,
	steven.price@....com,
	Barry Song <v-songbaohua@...o.com>,
	Chuanhua Han <hanchuanhua@...o.com>
Subject: [PATCH RFC 5/6] mm: rmap: weaken the WARN_ON in __folio_add_anon_rmap()

From: Barry Song <v-songbaohua@...o.com>

In do_swap_page(), while supporting large folio swap-in, we are using the helper
folio_add_anon_rmap_ptes. This is triggerring a WARN_ON in __folio_add_anon_rmap.
We can make the warning quiet by two ways
1. in do_swap_page, we call folio_add_new_anon_rmap() if we are sure the large
folio is new allocated one; we call folio_add_anon_rmap_ptes() if we find the
large folio in swapcache.
2. we always call folio_add_anon_rmap_ptes() in do_swap_page but weaken the
WARN_ON in __folio_add_anon_rmap() by letting the WARN_ON less sensitive.

Option 2 seems to be better for do_swap_page() as it can use unified code for
all cases.

Signed-off-by: Barry Song <v-songbaohua@...o.com>
Tested-by: Chuanhua Han <hanchuanhua@...o.com>
---
 mm/rmap.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index f5d43edad529..469fcfd32317 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1304,7 +1304,10 @@ static __always_inline void __folio_add_anon_rmap(struct folio *folio,
 		 * page.
 		 */
 		VM_WARN_ON_FOLIO(folio_test_large(folio) &&
-				 level != RMAP_LEVEL_PMD, folio);
+				 level != RMAP_LEVEL_PMD &&
+				 (!IS_ALIGNED(address, nr_pages * PAGE_SIZE) ||
+				 (folio_test_swapcache(folio) && !IS_ALIGNED(folio->index, nr_pages)) ||
+				 page != &folio->page), folio);
 		__folio_set_anon(folio, vma, address,
 				 !!(flags & RMAP_EXCLUSIVE));
 	} else if (likely(!folio_test_ksm(folio))) {
-- 
2.34.1